In the past, there is known an optical coordinate recognizing apparatus such as a touch panel including plural infrared light emitting elements arranged to be opposed to one another and infrared light receiving elements provided to respectively correspond to the light emitting elements.
In general, the optical coordinate-recognizing apparatus detects whether a light path formed between the light emitting element and the light receiving element, which form a pair, is blocked or not blocked and calculates coordinates, of the position of operation by a user on the basis of a result of the detection.
Specifically, the optical coordinate recognizing apparatus determines presence or absence of light blocking by comparing a difference between an output voltage of the light receiving element output while the light emitting element is on and an output voltage of the light receiving element output while the light emitting element is off and a predetermined reference value.
The accuracy of the coordinate recognition by the optical coordinate recognizing apparatus is deteriorated by the influence of disturbance light such as the sunlight or illumination. In order to reduce the deterioration in the accuracy of the coordinate recognition due to the disturbance light as much as possible, it is necessary to update, as required, the reference value to an appropriate value corresponding to an environment of use of the coordinate recognizing apparatus.